PROJECT SUMMARY Subcellular sequestration of second messenger-dependent mechanisms provides for specificity of signaling to discrete organelle systems or, in the case of polarized epithelial cells, plasma membrane domains. Multiprotein scaffolds coordinate cell-specific and intracellular location-specific signaling mechanisms. A kinase anchoring proteins (AKAPs) compromise the largest group of multifunctional scaffolding proteins, which anchor not only Type II cAMP- dependent protein kinase (PKA), but also a variety of protein kinases, phosphatases, phosphodiesterases and targets of second messenger regulated signaling. The AKAP350/450 gene codes for a number of different splice variants ranging from 250 to 450 kDa. AKAP350/450 splice variants potentially scaffold PKA, protein kinase C, PKN, casein kinase 1, phosphodiesterase 4D3, protein phosphatases 1 and 2a and calmodulin as well as a number of putative downstream effectors. AKAP350 is localized to both centrosomes and the Golgi apparatus, and we have demonstrated that depletion of AKAP350A with siRNA leads to disruption of the Golgi structure as well as alteration of polymerizing microtubules. Importantly, while previous investigations have focused attention on AKAP350 at the centrosome and the Golgi apparatus, our recent studies have led to the recognition that in most cells a large cytosolic pool of AKAP350 associates with CCAR1 and caprin and regulates mRNA trafficking and participates in microtubule-dependent stress granule formation. While we and others have demonstrated that AKAP350 can potentially scaffold a wide range of proteins, the actual composition of scaffolded complexes is likely both cell specific as well as subcellular organelle specific. The challenge of studying these large anchored multiprotein complexes is to discern the role of specific coordinated complexes in the regulation of intracellular processes. We have hypothesized that intracellular AKAP350-coordinated complexes regulate both trafficking through the Golgi apparatus and processing of discrete RNA species within cytosolic domains. To examine these hypotheses, we will pursue two specific aims. First, we will determine the role of AKAP350A and its associated proteins in regulating the structure and function of the Golgi apparatus. Second, we will investigate the role of the cytosolic pool of AKAP350A and its associated proteins in regulating RNA trafficking and translation. These studies will establish the roles of specific multiprotein complexes scaffolded by AKAP350 in localized regions of the cell.